1. Technical Field
The present invention relates in general to evaluating magnetoresistive elements and, in particular, to an improved system, method, and apparatus for electrically testing and monitoring lead-to-lead shorting during magnetoresistive sensor fabrication on a wafer.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm). Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile (2.5 and 1.8 inches) and microdrive.
A typical HDD also uses an actuator assembly to move magnetoresistive (MR) read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
A slider is typically formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track on a disk, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
As HDDs have improved in performance, the widths of the tracks on the MR elements or heads have decreased. This decrease in MR head track width has the inverse effect of increasing the processing complexity of the MR heads. One specific difficulty associated with narrow track widths is an increased likelihood in the formation of an electrical short between the leads of MR heads when they are formed on the wafers. An “electrical bridge” between the leads can degrade head performance by shunting current from the sensor. Therefore, early detection of lead-to-lead shorting provides critical process feedback in terms of yield and cost control.
The conventional technique used to detect MR head lead-to-lead shorting utilizes a top-down scanning electron microscope (SEM) image or photograph of each MR head on a wafer. The drawbacks for using these images to detect lead-to-lead shorting are twofold. First, only the images (i.e., not the heads themselves) are manually inspected to determine if lead-to-lead shorting is present. This inherently provides a merely subjective detection scheme, which can be misinterpreted by the operator. Second, the images cannot tell the operator if a lead-to-lead short is a high resistance short (and, therefore, “unimportant”), or an “important” low resistance short. Thus, it would be desirable to improve the electrical monitoring of lead-to-lead shorting during the wafer fabrication of magnetoresistive sensors.